Wire-shaped object



J 19, 1956 J. J. WENT ET AL WIRE-SHAPED OBJECT Filed Sept. 24, 1951 INVENTORS Roelof Vermeulen on dwen W RE-SHAPED. OBJECT Jan Jacobus. Went and Roelof Vermeulen, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust; Company, Hartford, Conn., as trustee pp a ion September 24,1951, Serial No. 243,042. Claims priority, application Netherlands. October-,3, 1 950 4. Claims. to]. 29-1912) The invention relates to wire-shaped objects comprising a core and a sheath arranged at a certain distance concentrically thereto, these two parts being preferably made of the same material, the space between the core and the sheath comprising a finely divided powder. It is known to use such an object, in which the powder is made of electrically insulating material, for example as a resistance wire in resistors, an indirectly heated cathode in a highvacuum tube, or as wire capacitors. The construction described makes it possible to manufacture wires of a few tenths of millimeters in thickness in a comparatively simple and cheap manner, i. e. by a series of mechanical operations such, for example, as hammering and subsequent drawing or rolling.

According to the invention the powder is made of permanently magnetizable, ferromagnetic material, the mau terial for the core and the sheath is aluminium or a material, for example a weak kind of copper similar to the former as regards deformability in the cold state and mechanical strength. Apart from the advantages inherent in the known method of manufacturing there is the advantage that owing to the construction, the object according to the invention is particularly suitable to be used as a carrier of magnetic records. In the present case the choice of the sheath material from the series of materials suggested before, for example, nickel, molybdenum or aluminium, is based on the recognition of the fact that during the mechanical operations the intermediate heattreatments of the Wire as are required with other sheath materials such as nickel or molybdenum should not detract from the magnetic properties of the powder. Since aluminium is deformable in cold condition to the degree required for the present case, without becoming brittle and without being cracked or broken, it is well suited for use as sheath material for carriers of magnetic records according to the invention. The use of a weak kind of copper may require an intermediate heat-treatment; in this case the temperature should not exceed 150 C. in order to avoid sintering of the powder and hence a diminution of the magnetic properties. In order to obtain the same advantages for the core and to avoid diificulties in the drawing operation, the core is made of the same material as used for the sheath.

With the object according to the invention and in contradistinction to the known strip-like carriers of magnetic records in which ferromagnetic powder is provided on or in the carrier, the ferromagnetic powder layer to be used for recording or to be provided with records is protected by a sheath. The provision of the sheath has a further advantage in that a binder is not required, so that the filling factor of the space between the core and the sheath may be very high. Since wire-shaped carriers of magnetic records are known to be wound on a reel, the known wire-shaped carriers, in which the ferromagnetic material forms the sheath, bring about the risk of cross-talk owing to the relative contact between adjacent turns. With the wire-shaped carriers according to the invention this disadvantage is sharply reduced, since the magnetic layers nited States PatentQ f adjac n rns a s parat d. by l y o non-m gnetic he th. mate ial.

If it is desired to. manufacture wire-shaped objects a cord ng t he invention wi h th QOnventiQIlfl diam te of wire-shaped carriers of magnetic records lying bet "een 0.2 and 0.05 mm. and with a magnetic powder havlng a coercive force of at least 300 oersted, the powder according to h i ention h s Par i e mag itude not more than 2 the thickness of the layer being about one en h of h ter wire ame r- Th ch i e m n mum value of the coercive force is connected with the well-known fact that at high frequencies the recording sensitiveness increases with an increasing value of the coercive force. The choice ofthe thickness of the powder yer is on ected th, h ne d o ha n the g a pos l mogenei y of. the stray fie dof he. record head throughout the thickness of the magnetic layer.

In spite of the strong relative magnetic efiect of the particles of the aforesaid magnitude relative to one another which is due to the high coercive force, it has been found that the construction and the manufacturing method of the wire, in which the powder layer is strongly compressed, permits of obtaining a very homogeneous distribution of the particles. Such a homogeneous distribution of the particles having the aforesaid coercive force has not yet been obtained with other carriers of magnetic sound records, so that one had to be satisfied either with the use of particles having a lower value of coercive force in order to ensure a sufficiently homogeneous distribution, or with a higher noise level due to a less homogeneous distribution with the use of particles having a coercive force of a value as referred to in the present case.

In addition to the advantage of a high coercive force owing to the small particle size, the use of particles smaller than 2 1. in a wire having an outer diameter of between 0.2 and 0.05 mm., in which the layer thickness is onetenth of the outer diameter, has the advantage that a comparatively great plurality of particles may be provided in the layer. An excessively small plurality of particles per unit of length of the Wire would harmfully aifect the noise. It will be obvious that in each case in practice with a particular wire diameter the maximum particle size and the layer thickness have to be adjusted to one another, in accordance with the noise required.

It should be noted that it has been known that the separate particles may have an extremely high coercive force, if iron, iron alloys, nickel, cobalt and so forth or oxides thereof are in a very finely divided condition with a particle size of less than 2,u.. It is known to utilize this particle size with the manufacture of powdery magnets and to mould the powder in the desired shape at a temperature at which sintering does not occur. It is furthermore known to use such powdery materials on or in stripshaped carriers of magnetic records. However, in this case it is found that, as stated above, one has to be satisfied either with a lower value of the coercive force of the particles or with a higher noise level. Carriers according to the invention in which use is made of the said powdery materials, are free from these disadvantages, since owing to the construction of the carrier the particles are strongly compressed in a very homogeneous distribution without the use of a binder.

In order that the invention may be more clearlyunderstood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, in which one embodiment of the carrier according to the invention is shown.

The drawing shows a core 1 of pure aluminium and a sheath 2 arranged to surround the core concentrically at a certain distance and made of the same material, the space between the two parts being filled up with powdery iron 3. The outer diameter of the sheath was initially 7.2 mms., the inner diameter 6.2 mms., Whereas the core diameter was 3 nuns. Subsequent to the rolling and drawing operations the sheath had an outer diameter of 0.1 mm. and an inner diameter of 0.078 mm. The core had a diameter of 0.050 mm., so that the thickness of the powder layer was 0.014 mm. The powder particles had a size of about 0.03 to 0.05;; and the powder layer had a coercive force of 1100 oersted. A Wire manufactured in this manner may readily be twisted into a knot.

What we claim is:

1. A wire-shaped magnetic record carrier comprising an aluminum core, a concentric aluminum sheath spaced from said core and defining an annular space therebetween, and a finely divided permanently magnetizable ferromagnetic material filling said annular space.

2. A wire-shaped magnetic record carrier as claimed in claim 1 in which the ferromagnetic material is powdered iron having a particle size not exceeding 2pc.

3. A wire-shaped magnetic record carrier as claimed in claim 2 in which the ferromagnetic material has a coercive force of at least 300 oersted.

References Cited in the file of this patent UNITED STATES PATENTS 978,847 Carlisle Dec. 20, 1910 1,580,647 Breck -Q. Apr. 13, 1926 1,792,377 Jordan Feb. 10, 1931 1,883,559 Chipman Oct. 18, 1932 1,892,607 Bundy Dec. 27, 1932 2,087,051 Stargardter July 13, 1937 2,172,207 Kolligs Sept. 5, 1939 2,290,967 Herriger July 28, 1942 2,459,161 Harris Jan. 18, 1949 2,509,117 Wallace May 23, 1950 2,619,454 Zapponi Nov. 25, 1952 

